China DOS Union

Of course not. But you can use the SUBST command to make a huge “floppy disk” to install certain software. Or make the path for some software shorter so it's easier to run.

subst is used to virtualize a directory on the hard disk as a floppy disk

If the target drive being virtualized is gone or the files are deleted, will it affect the virtual drive? And can you delete files in the virtual drive and use it as if it were a hard disk?

What SUBST virtualizes still counts as a hard disk, I guess, but it is definitely not a real hard disk. When the actual one is deleted, the virtual one is gone too. More precisely, SUBST is a drive-letter relocator; it only maps the drive letter, that's all.

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The program file for the Subst command, Subst.exe, is stored in the “C:＼Windows＼Command” folder. Its function is to make a drive letter equivalent to a specified folder, that is, to use a disk drive letter in place of a folder name. The format is as follows:

　　Subst

　　Where: “Drive1:” is the virtual drive letter assigned to replace the folder, and “Drive2:＼Path” is the folder and path to be replaced. The command “subst a: d:＼mydisk” virtualizes the folder “d:＼mydisk” as drive A. To delete the virtual drive letter, execute “Subst Drive1: /D” in DOS mode. For this example, the steps to delete the virtual drive letter are as follows:

　　1. Click “Start→Programs→MS-DOS Mode” to open a DOS window.

　　2. At the DOS prompt, type the command:

　　subst a: /D

Thanks to all the experts for the explanations!

I think a simpler explanation is this:
If you install a virtual CD-ROM drive on your hard disk,
does your hard disk space become larger?
Obviously not, unless you've never installed one before